European patent no. EP-0170375 describes a sample collecting and testing device with a cavity which has dimensions small enough to enable the sample liquid to be drawn into the cavity by capillary action. Each cavity includes an electrode structure for making measurements of one or more electrically measurable characteristics of the sample.
Such capillary fill cells have the disadvantage of requiring the cell to have an exact depth which must be small enough to allow the capillary action. If the liquid sample is dirty or viscous, the contact angle between the cell and the liquid is destroyed and capillary action does not result. If the cell is immersed too far into the sample liquid, the sample can enter both ends of the cell and this can result in a bubble forming within the cell negating the measurement. Furthermore, for some forms of liquid sample, a surfactant is required to increase the capillary action.